Battery with complete discharge device

ABSTRACT

A battery having a complete discharge mechanism includes a spring-biased switch with an element spring-biased from the switch and acts to close the switch when in a fully extended position. A block is position above the element with a passageway aligned with the element. A flexible positioned between the element and the passage prevents the element from extending into the passage. The tab extends through the battery casing. When pulled the tab allows the element to extend into the passage thereby closing the spring-biased switch and completing the discharge circuit.

BACKGROUND OF THE INVENTION

Discarded partially discharged batteries can present a significantdanger. Alkali metal batteries present a particular problem. Because thealkali metal such as lithium will burn when exposed to water, apartially discharged battery presents a significant concern.

In order to address this issue, many lithium batteries incorporate acircuit to completely discharge the battery. After the battery hasdischarged to the point where it is no longer useful, the completedischarge circuit is activated, totally consuming the lithium, therebyreducing or eliminating any fire hazard.

One such device is disclose in McCaleb U.S. Pat. No. 5,119,009. Thispatent discloses a one-time switch used to close a complete dischargecircuit. It requires that a pointed object push a switch element intothe battery casing, closing the one-time switch. The battery thencompletely discharges and can be safely disposed.

Sink et al U.S. Pat. No. 6,270,916 utilizes a different dischargecircuit. Instead of a switch, it uses a spring clip which contacts aconductor, closing the circuit. In order to prevent discharge, aninsulating strip is place between the clip and the conductor. When it isdesired to discharge the battery, the strip is removed, the spring clipthen makes contact with the conductor, and the battery discharges. Thishas the advantage of not requiring a separate device to close theswitch.

If the spring clip is not properly biased, the proper contact will notbe made. Further, if the insulator strip is improperly positioned, itcan cause a premature discharge of the battery. Moisture can also causethe circuit to close.

SUMMARY OF THE INVENTION

The present invention is premised on the realization that a completedischarge device (CDD) for a battery, in particular a lithium battery,can employ a spring biased switch. A spring biased switch has an elementwhich, when in an extended position, is closed. The device also includesa block or other structure that has a bore or opening that aligns withthis spring biased element. A tab inserted between the spring biasedelement of the switch and the opening in the block prevents thespring-biased element from extending outward and keeps the switch on thecomplete discharge device in an open position. When the tab is pulled,the spring in the switch forces the element outward, thereby closing theswitch and activating the complete discharge device. Preferably, theelement is simply a post.

The invention will be further appreciated in light of the followingdetailed description and drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a battery incorporating the presentinvention.

FIG. 2 is a perspective view partially broken away showing the switchmechanism according to the present invention in the closed position.

FIG. 3 is an alternate embodiment of the device shown in FIG. 2 with theswitch in the open position.

FIG. 4 is a circuit diagram showing a complete discharge circuit.

DETAILED DESCRIPTION OF THE DRAWINGS

As shown in FIGS. 1 and 2, the complete discharge circuit 10 of thepresent invention is encased within a battery 11 and designed to connecta load across the cell strings of a battery, thereby discharging itcompletely. The battery 11 includes a top wall 13 having positive andnegative terminals 16 and 17. The complete discharge switch 12 islocated on the inside surface 19 of front wall 13 of the battery. Theswitch 12 can be located on the inside surface of any exterior wall ofbattery 11 or on a printed circuit board mounted within a battery andlocated where a tab 24 can be extended through an exterior wall.

Switch 12 of circuit 10 includes a plunger element 14 spring biased inthe direction of arrow 16. Element 14 is shown partially in phantom inthe Figures. This element 14 is aligned with an opening 18 between twoblocks or obstructions within the battery 11. The opening can beestablished by a structure 21 having blocks 21 a and 21 b as shown inFIG. 2, or, as shown in FIG. 3, can actually be two electricalcomponents 20, 22 such as capacitors, resistors, or the like, which formpart of the circuitry on the inside surface of wall 13. This surface 19as shown is a circuit board which incorporates the CDD circuit.

As shown in FIG. 3, the switch is held in an open position by a pull tab24 of a thermally stable yet flexible material such as polyester. Thisextends from the exterior of the battery through a slot 27 in thebattery and slot 26 in surface 13 of circuit board 19 between blocks 21a, 21 b and switch 12. Thus, tab 24 blocks the opening 18 and preventsthe element 14 from moving in the direction of arrow 16.

On the exterior of battery 11, the tab 24 is held in place by a piece ofpressure sensitive tape 25 to avoid inadvertent pulling and thusdischarge of the battery 11. Other protective measures can also beemployed such as a plastic cap or application of pressure sensitiveadhesive to the exterior surface of tab 24 to adhere this portion to theexterior surface of battery 11.

To activate the complete discharge circuit, tape 25 is removed and tab24 is pulled. As shown in FIG. 2, element 14 then moves into opening 18,thereby closing the switch and closing the circuit 10 causing the deviceto discharge completely. The discharge is controlled by circuit 10 toallow a controlled discharge of the battery so that excess heat is notgenerated and fire danger is reduced. A constant resistance circuit isshown. A constant current discharge can also be employed, if desired.

This system eliminates the problems associated with using simply aninsulator between two conductors and yet provides a simple, easy methodfor activating a complete discharge circuit.

Having described this invention, its advantages and parameters, it willbe obvious to a person of ordinary skill in the art, in view of theabove description, that variations thereof may be made without departingfrom the spirit and scope thereof.

1. A battery having a complete discharge mechanism; said mechanismincluding a switch having a spring-biased element wherein said elementacts to close said switch when said element is fully extended; a passagealigned with said element and adapted to receive said element; a tabpositioned between said element and said passage, said tab preventingsaid element from extending into said passage; and said tab extendingthrough a casing of said battery; whereby pulling said tab allows saidelement to enter said passage and close said switch thereby activatingsaid complete discharge mechanism.
 2. The battery claimed in claim 1further comprising two spaced blocks creating said passage and said tabextends between said blocks.
 3. The battery claimed in claim 2 whereinsaid blocks are electrical components.
 4. The battery claimed in claim 2wherein said switch and said electrical components are positioned on acircuit board mounted within said battery and wherein said tab extendsthrough a slot in said battery.